Apparatus of this type are used in particular, although by no means exclusively, for mechanically folding bed sheets so that these can be packed in packet form. After the bed sheets have been cut to size and sewn, the lengths of fabric, which are spread out flat, are fed into a lengthwise folding device in which they are folded to produce a tubular folded product with lengthwise folding edges extending substantially parallel to one another. The basic structure of folding devices of this kind is known from the prior art. The tubular folded product is then conveyed into a crosswise folding device in which it is folded with crosswise folding edges extending substantially perpendicularly to the lengthwise folding edges. The folded product is thus given the desired packet form in which it can sequently be packed.
A stop strip, against which the tubular folded product comes to lie, at least in certain regions, before being folded, is disposed in the crosswise folding device. The stop strip forms an end stop for the conveying movement of the folded product when the latter is fed into the crosswise folding device and ensures that it has a defined orientation before crosswise folding takes place.
A drawing device is disposed in the crosswise folding device in the region between the two ends of the tubular folded product in order to draw in the folded product for crosswise folding. After the folded product has been conveyed completely into the crosswise folding device and come to lie in a defined manner against the stop strip, it is drawn in by the drawing device in the central region, whereby the first crosswise fold is formed and the folded product therefore folded crosswise once.
The disadvantage of known folding apparatus lies in their inadequate folding accuracy in crosswise folding in the crosswise folding device. Since a plurality of fabric layers already lie on top of one another as a result of the lengthwise folding process in the lengthwise folding device, the folded product tends to become distorted in the drawing-in region when being drawn into the drawing device such that the free ends of the folded product, which have not yet been drawn in, are displaced horizontally. Due to this shifting of the free ends of the folded product, the lengthwise edge of the folded product no longer lies properly against the stop strip while being drawn in. As a result, the folded product is no longer drawn evenly into the drawing device parallel to the stop strip, so that considerable folding inaccuracies arise when folding crosswise, in particular in subsequent folding stages. The distortion of the folded product in the drawing-in region increases with the number of fabric layers lying on top of one another. The unwanted distortion of the folded product may be increased even further if the two lengthwise edges ofthe tubular folded product have different layer thickness, i.e. a different number of fabric layers lying on top of one another.